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Method and apparatus for modulating and demodulating data into a variable length code and a providing medium for implementing the methodRelated Patent Categories: Pulse Or Digital Communications, Pulse Code Modulation, Length CodingMethod and apparatus for modulating and demodulating data into a variable length code and a providing medium for implementing the method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070014370, Method and apparatus for modulating and demodulating data into a variable length code and a providing medium for implementing the method. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a modulation a data-modulating apparatus, a data-modulating method, a data-demodulating apparatus, a data-demodulating method, and a data-providing medium. Particularly, the invention relates to an apparatus and method for modulating data to transmit the data or record the data on a recording medium, an apparatus and method for demodulating data that has been modulated, and a medium for use in transmitting or recording data that has been modulated. BACKGROUND ART [0002] Data is modulated to be transmitted via a predetermined transmission path or recorded on a recording medium such as, for example, a magnetic disk, an optical disk or a magneto-optical disk. Known as one of such data-modulating methods is block encoding. In the block encoding, a row of data is divided into blocks, or units each consisting of m.times.i bits. (Hereinafter, the units of data will be referred to as "data words.") The data words are modulated to code words, each consisting of n.times.i bits, in accordance with an appropriate encoding rule. Each code word has a fixed length if i is one (1). It has a variable length if the value i can be selected from a plurality of values. That is, the code word has a variable length when one of values ranging from 1 to imax (the greatest value for i) is selected for i. The code generated by the block encoding is a variable-length code (d, k; m, n; r). [0003] It should be noted that the value i is called "constraint length", and the value imax is called "maximum" constraint length r. The minimum run d indicates the least number of ones (1s) that may be included in a train of codes. The maximum run k indicates the greatest number of ones (1s) that may be included in a train of codes. [0004] To record variable-length codes generated as described above, on a compact disk, a mini-disk or the like, NRZI (NonReturn to Zero Inverted) modulation on the variable-length codes. In the NRZI modulation, the variable-length code is inverted at each one (1) and not inverted at each zero (0). The variable-length codes subjected to the NRZI modulation (hereinafter referred to as "level codes " are recorded on the disk. [0005] Inverse NRZI modulation, wherein a level code is changed to when is inverted to "0" or "0" is inverted to "1", thereby becoming an edge, may be performed on variable-length codes. In this case, a train of codes identical to original EFM codes or RLL (1-7) codes can be obtained. These inverse NRZI codes are called "edge codes." [0006] Let the minimum interval of inverting level codes be Tmin, and let the maximum interval of inverting level codes be Tmax. In order to record data at high density in the linear velocity direction, it is desired that the minimum code-inverting interval Tmin be long. That is, the minimum run d should be large. In order to reproduce clock signals, it is desired that the maximum code-inverting interval Tmax be short. In other words, the maximum run k should be small. In view of this, various data-modulating methods are proposed. [0007] One example is the data-modulating method known as RLL (1-7) that is used to record data on a magnetic disk, a magneto-optical disk or the like. The parameter for this data-modulating method is (1,7:2,3; 2). The minimum code-inverting interval Tmin is 2 T, or (1+1)T. This minimum code-inverting interval Tmin is 1.33 Tdata, i.e., (M/n).times.Tmin=(2/3).times.2. The maximum code-inverting period Tmax, given as (k+1)T, is 8, or (7+1)T=2/3.times.8 Tdata=5.33 Tdata. The width Tw of the detection window, given as (m/n)T, is 0.67(=2/3) Tdata. [0008] The conversion table for RLL (1-7) codes is, for example, a table shown in the following Table 1: TABLE-US-00001 TABLE 1 RLL (1, 7; 2, 3; 2) Data Decode i = 1 11 00x 10 010 01 10x i = 2 0011 000 00x 0010 000 010 0001 100 00x 0000 100 010 [0009] Symbol x used in the conversion table is "1" when the next channel bit is "0" and is "0" when the next channel bit is "1". The maximum constraint length r is 2. [0010] In the train of channel bits, which has been modulated by the method RLL (1-7), 2 T occurs most frequently at interval Tmin, 3 T occurs less frequently than 2 T, and 4 T occurs less frequently than 3 T. If the data items such as 2 T or 3 T occurs at high frequency, it helps to reproduce clock signals. If 2 T occurs continuously, however, its waveform recorded may likely to be deformed. (The waveform output of 2 T is small and is easily influenced by either defocusing or tangential tilt.) Further, smallest marks recorded continuously in high linear density may likely be influenced by external disturbance such as noise, causing errors in the data that will be reproduced. [0011] The applicant hereof proposed in Japanese Patent Application No. 9-133379 that Tmin be prevented from occurring more frequently than a prescribed times. The conversion table for RLL (1-7) codes for use in this proposed method is, for example, the following Table 2. TABLE-US-00002 TABLE 2 RML (1, 7; 2, 3; 3) Data Codes i = 1 11 00x 10 010 01 10x i = 2 0011 000 00x 0010 000 010 0001 100 00x 0000 100 010 i = 3 100110 100 000 010 [0012] Symbol x used in this conversion table is "1" when the next channel bit is "0" and is "0"when the next channel bit is "1". The maximum constraint length r is 2. [0013] In the conversion achieved by using Table 2, the next four data items are referred to when the data row becomes "10", and a code "100 000 010" for preventing the repetition of the minimum run d is given when the data row of six bits becomes "100110". The minimum run d may be repeated six times at most in the code obtained by this conversion. [0014] To record data on a recording medium or transmit data in a specific way, the data is modulated into codes that can be recorded on the medium or transmitted in that specific way. The modulated codes may contain a direct-current component. If so, various error signals, such as the tracking error signal for the servo control in a disk drive, are likely to change or contain jitter. Therefore, the modulated codes should not better contain a direct-current component. [0015] The variable-length RLL codes mentioned above, in which the minimum run d is 1 (d=1) and the conversion rates m and n are 2 and 3 (m=2, n=3), are not subjected to DSV (Digital Sum Value) control. In the DSV control, the absolute value of the total sum (DSV) of codes is decreased, when the train of channel bits is subjected to the NRZI modulation (that is, converted to level codes), and the "1 " bits of the train (data symbols), i.e., +1 codes, are added, whereas the "0" bits of the train, i.e., -1 codes, are added. The DSV can serve to estimate the direct-current component in the train of codes. To decrease the absolute value of the DSV is to reduce the direct-current component in the train of codes. [0016] In most cases, 2.times.(d+1) bits are used as DSV control bits. If d=1, four bits, i.e., 2.times.(1+1) bits, will be used as DSV bits. In this case, the minimum run and the maximum run can be maintained, and perfect DSV control can be achieved to invert codes and not to invert codes at any given intervals. [0017] However, the DSV control bits are basically redundant bits. It is there desirable that the DSV control bits be reduced in number as much as possible in view of the efficiency of inverting codes. [0018] Alternatively, 1.times.(d+1) bits may be used as DSV control bits. If so, two DSV bits, i.e., 1.times.(1+1) bits, will be used. In this case, too, perfect DSV control can be accomplished to invert codes and not to invert codes at any given intervals. Nonetheless, the maximum run increases to (k+2), though the minimum run can be maintained. The minimum run must be preserved by all means as a recorded code, but the maximum run need not be preserved as such. In some cases, there are formats in which a pattern breaking the maximum run is used as a sync signal. (EFM plus of DVD has a maximum run of 11 T, which may increase to 14 T to use a specific format.) [0019] A table of 1,7PP (Parity preserve Prohibit rmtr) codes is available as a table that can achieve DSV control more efficiently, while preserving the basic function of the RML codes shown in Table 2. The 1,7PP codes are modulated codes, wherein the minimum run is 1 (d=1) and the maximum run is 7 (k=7). In each 1,7PP code, the minimum run is prohibited from repeating itself and rule is imparted to the elements that correspond to data words and code words. [0020] The conversion table for 1,7PP codes, which the applicant hereof proposes in Japanese Patent Application No. 10-150280, is, for example, the following Table. TABLE-US-00003 TABLE 3 1, 7PP (1, 7; 2, 3; 4) Data Code 11 *0* 10 001 01 010 0011 010 100 0010 010 000 0001 000 100 000011 000 100 100 000010 000 100 000 000001 010 100 100 000000 010 100 000 "110111 001 000 000(next 010) 00001000 000 100 100 100 00000000 010 100 100 100 if xx1 then *0* = 000 xx0 then *0* = 101 "110111 001 000 000(next 010): When next channel bits are `010`, convert `11 01 11` to `001 000 000` after using main table and termination table. [0021] In Table 3, the minimum run is 1 (d=1) and the maximum run is 7 (k=7). Among the elements sown in this conversion table are uncertain codes. An uncertain code is either "000" or "101" if two bits of the data row to be converted are (11), depending upon the code word train that immediately precedes the data row. If one channel bit of the immediately preceding code word train is "1", the two bits (11) will be converted to "000" to preserve the minimum run. If one channel bit of the immediately preceding code word train is "0", the two bits will be converted to "101" to preserve the maximum run. [0022] The conversion table of Table 3 is one having a variable-length structure. That is, a code to be converted at the constraint length i=1 is composed of three data items, less than the four data items required [2 (m.times.i)=2 (2.times.1)=4]. Namely, among the data rows to be converted is a data row that cannot be converted at the constraint length i. After all, the constraint length i=3 must be applied to use Table 3 as a conversion table, or to convert all data rows. Continue reading about Method and apparatus for modulating and demodulating data into a variable length code and a providing medium for implementing the method... 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